ch 13a, 13b unit 3 micro

capsid

protective protein coat

nucleic acid of virus

either RNA or DNA

nucleocapsid

the capsid and nucleic acid contents

tail

long helical protein component used for attachment to host cells

spike proteins

project from capsid in tailless viruses

needed for attachment to host cells

envelope

lipid bilayer derived from the host cell that surrounds the capsid.

Found only in animal viruses.

Viruses without an envelope are called “naked”

naked virus

no envelope

viral attachment

can only enter host cells that express specific proteins on their surface

like a key to a lock

virus attaches to receptor protein and insert its genetic information into host cell

phage attachment

phage attaches to specif protein receptors of host

genome entry (phage)

tail contracts and phage DNA is injected into bacterial cell

phage coat left outside

synthesis (phage)

phage genome is transcribed phage proteins synthesized

DNA is replicated, other virion components made

host DNA degraded

assembly (phage, step 4)

phage components assembled into mature virions

release

bacterial cell lyses and new infectious virions are released

step 5

lytic (phage)

viruses that lyse the host cell every time they are released

also called virulent phages

filamentous (phage)

viruses that leak out of extrude without killing host cells

temperate (phage)

viruses that integrate their DNA into the genome of the bacteria they infect

or DNA replicates as a plasmid

90% of all viruses are __ phages

prophage

a bacteriophage (virus) genome that has integrated into a bacterium's chromosome or exists as an plasmid, residing in a dormant, non-infectious state known as lysogeny

lysogenic state

virus is incorporated into the host DNA

lysogenic conversion

a process where a bacterium acquires new, inheritable genetic traits—often increased virulence—by integrating DNA from a temperate bacteriophage into its own genome

transduction

bacterial viruses (bacteriophages) mistakenly carry bacterial genes from one host to the next

Generalized transduction

—any genes of the donor cell can be transferred.

An error occurs during construction of the virus and a fragment of bacterial DNA is packaged in the protein coat of the virus.

Specialized transduction

only a few specific genes can be transferred.

This is carried out by only temperate phages

Generalized transduction temperate phages

performed by virulent and temperate phages

recipient host cell is not lysed because the genetic information within the new phage is incomplete.

specialized transduction temperate phages

only bacterial genes located near the prophage on the chromosome may be transferred to the next host cell.

limited to a single bacterial species and often to only a few strains of that species

what is the host range of phages?

mainly in cell wall but sometimes

pili

flagella

where are the receptors located for phage attachment

Naked viruses

no envelope, just nucleocapsid.

Spike proteins are on the capsid

Enveloped virus

nucleocapsid surrounded by lipid membrane.

Spike proteins are on the envelope

only on animal viruses

envelope

what do phages lack compared to animal viruses?

segmented viruses

RNA viruses with genomes divided into multiple, distinct linear molecules, rather than a single molecule

• ex influenza has 8 RNA molecules

attachment (animal virus)

virus attaches to specific receptor proteins on the host cell surface

entry (animal virus)

Naked viruses enter the host cell through endocytosis

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Enveloped viruses enter through fusion of the envelope with the host cell plasma membrane

Both capsids enter host cell

Uncoating (animal virus)

The nucleic acids are released from the capsid

step 3

Replication (animal virus)

RNA/DNA is replicated. Proteins are produced in the form of polyproteins

which must be cleaved by viruses-encoded protease to function.

Inhibited by protease inhibitor drugs

step 4

Assembly (animal virus)

insertion of nucleic acid into protein coat

step 5

Release (animal virus)

step 5

—Naked viruses are released from the cell by lysis.

Enveloped viruses are released through the process of budding.

Retroviruses

single-stranded enveloped RNA viruses.

Most prominent of this class of virus is HIV

Reverse transcriptase

an enzyme that is contained in the capsid of retroviruses and is responsible for converting the RNA genome into DNA.

RNA→ DNA

Retroviruse RNA

RNA genome of a retrovirus must first be converted to a DNA copy for the virus to be replicated

• DNA copy is then integrated into the host genome

• From here, viral genes are expressed and the virus is reproduced

RNA→DNA→DNA in host genome→Virus replicated

Acute Infections

relatively short duration (generally less than 2 weeks).

• Virus disappears after disease ends, and is no longer detectable in any tissue of the host organism’s body

• ex influenza, mumps, polio

Persistent Infections

the viruses or their genomes are continually present in the body and virions are released from infected cells. 3 categories

virus is continually replicating

1. —Latent Infection

2. —Chronic Infection

3. —Slow Infection

latent infection

a type of infection where a pathogen (usually a virus or bacteria) resides in the body in a dormant, inactive state without causing symptoms or active disease

• infection is beat by host immune system but reactivated later due to hiding in nerve cells

ex Herpes Simplex 1 and 2, Varicella-Zoster, Epstein-Barr

Chronic Infections

long-term, persistent illnesses where the immune system fails to eliminate the virus

• virus demonstrated at all times

• Disease symptoms may be present or absent during an extended period of time, or may develop late

• ex —Hepatitis B, Hepatitis C

Slow Infections

Following initial infection, the infectious agent gradually increases in amount over a very long time (years) during which no significant symptoms are apparent

• eventually a slowly progressive lethal disease ensues

• ex HIV

• latent

mechanism is integration of a DNA virus into the host chromosome followed by expression of oncogenes

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Oncogenes are often altered forms of normal cell’s genes coding for proteins involved in regulating cell growth

• results in uncontrolled growth of host cells

what is the most common mechanism where viruses cause 20% of all human tumors?

—Hepatitis B/C- hepatic carcinoma

—Human Papillomaviruses- cervical, penile, anal cancers

Human Herpes Virus 8- Kaposi’s sarcoma (cancer of skin and internal organs, common in AIDS patients

what viruses are associated with tumor development?

uses hemagglutinin

What does influenza do to attach to host cells?

Antigenic drift is the accumulation of minor mutations in the hemagglutinin protein of the influenza virus. These small changes alter the virus enough that the immune system does not recognize it from previous infections, allowing the flu to infect people again in later seasons

What is antigenic drift and why does it allow the flu to infect people in consecutive years?

Antigenic shift occurs when genetic reassortment between two viruses infecting the same cell results in a new virus with different hemagglutinin genes, allowing it to evade existing human antibodies.

What is antigenic shift in influenza viruses?

Antigenic shift creates major changes in influenza surface antigens through gene segment reassortment, producing a virus that human populations have little or no immunity to, leading to pandemics every ~10–30 years.

Why can antigenic shift lead to influenza pandemics?

Feature	Antigenic Drift	Antigenic Shift
Type of change	Minor mutations	Major genetic change
Mechanism	Point mutations in hemagglutinin genes	Genetic reassortment between different viruses
Frequency	Happens continually	Occurs every 10–30 years
Result	Seasonal flu infections	Pandemics
Immunity	Partial immune recognition	Little to no population immunity

What is the difference between antigenic drift and antigenic shift in influenza viruses?

Hemagglutinin (HA) is a surface glycoprotein on the influenza virus that binds to receptors on host cells, allowing the virus to attach and enter the cell.

What is hemagglutinin (HA) in the influenza virus?

Viruses must be cultivated in host cells because they can not multiply themselves

what is the method on how to study viruses?

Primary tissue culture (viral growth method

tissue cultures prepared directly from the tissues of an animal.

Cells die after 50-100 division, so new primary cultures must be continually started

Cell lines (viral growth method

tissue cultures prepared from tumor cells. Tumor cells multiply indefinitely.

However, conclusions about “normal cells” can not be made

Embryonated chicken eggs (viral growth method)

used to grow influenza

Living animals (viral growth method)

necessary for some virus strains

A plaque assay measures the number of infectious virus particles in a sample.

A virus solution is added to a monolayer of host cells, where infection and cell lysis create clear zones called plaques.

• each plaque represents one virion

what is Plaque Assay and what does it quantify

Hemagglutination occurs when some viruses bind to and clump red blood cells (RBCs) by attaching to receptors on multiple cells.

• Caused by viral surface proteins (e.g., hemagglutinin in influenza)

• Measured using serial dilutions of a virus mixed with RBCs

• Virus titer = highest dilution that still shows agglutination

What is hemagglutination and how is it used to measure virus concentration?

1. —Attachment

2. —Entry

3. —Replication (DNA/RNA created)

4. —Assembly

5. —Release (naked lyse, enveloped bud)

what are the steps of animal virus replication?

viroid

small, circular, single-stranded RNA molecules that lack a protein coat

infect only plants!

Prions

infectious particles that contain ONLY protein (no nucleic acids)

Infectious prions

similar structure to normal prions, but mutation has caused the protein to have a different folding pattern.

mutant prion is resistant to protease

Normal prion

proteins found in brains of all vertebrates.

—replicates by converting the normal host protein into mutant prions by altering its folding pattern.

how do prions multiply?

spongiform encephalopathies (holes in brain)

what do prions do to tissue?

when prions aggregate in insoluble masses (plaques) outside the nerve cells. Nerve cell death results.

prion disease is caused by

Scrapie

—Mad Cow Disease

—Chronic Wasting Disease

—Creutzfeldt-Jakob Disease

—Kuru

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Cause

behavioral changes, anxiety, insomnia, fatigue, muscle jerks, lack of coordination, dementia, and death

what are the 5 prion diseases?

• Attachment (cell wall)

• Genome entry

• synethesis

• assembly

• release

what are the steps in phage replication?

virulent(lytic) and temperate phages

generalized transduction is preformed by

Hep B

Chronic,

Affects- Hepatocytes

causes- hepatitis, cirrhosis, hepatocarcinoma

Hep C

Chronic,

Affect- Hepatocytes

causes- hepatitis, cirrhosis, hepatocarcinoma

Herpes simplex type I

Latent

affects neurons of sensory ganglia

causes- oral herpes

Herpes simplex type 2

latent

affects- neurons of sensory ganglia

causes- genital herpes

varicella zoster (chickenpox)

Latent

affects- sensory ganglia cells

causes- chickenpox and shingles

cytomegalovirus

Latent

affects- salvary glands, kidneys, and leakocytes

Causes- pneumonia, eye infection

epstein-Barr virus

latent

causes- B lymphocytes

disease- mononucleosis

Human immunodeficiency virus (HIV)

Chronic/slow

Affects- T lymphocytes

causes- AIDS